Role of dispersion state of ti species in deactivation of MgCl2-supported Ziegler-Natta catalysts

Abstract

The deactivation behaviors of TiCl 3 /MgCl 2 model catalysts with molecularly dispersed TiCl 3 were investigated to clarify the role of the dispersion state of the Ti species in the deactivation of MgCl 2 -supported ZieglerNatta (ZN) catalysts for propylene and ethylene polymerization. The propylene and ethylene polymerization activities of clustered Ti species supported on MgCl 2 were approximately one tenth of those of isolated Ti species, which is indicative of the significance of the aggregation of Ti species in the deactivation of ZN catalysts for olefin polymerization. Moreover, the time-course depression of monomer consumption for the clustered Ti species was slower than that for the isolated Ti species in propylene polymerization, whereas the dispersion state barely affected the depression rate in ethylene polymerization. The reduction rate of the Ti species was concluded to be important for the time-course depression of propylene consumption, whereas ethylene polymerization was insensitive to the oxidation state of the Ti species.

Precise Active Site Analysis for TiCl3/MgCl2 Ziegler-Natta Model Catalyst Based on Fractionation and Statistical Methods

“…The catalysts are generally composed of a solid component (TiCl 4 /MgCl 2 /internal donor) and an activator component (alkylaluminum/external donor). Alkylaluminum activates TiCl 4 through reduction and alkylation to initiate polymerization.…”

“…Alkylaluminum activates TiCl 4 through reduction and alkylation to initiate polymerization. The high OPEN ACCESS reactivity of alkylaluminum also causes the deactivation of catalysts, which go through the overreduction and agglomeration of Ti species [1][2][3][4], as well as the removal of donor molecules from surfaces. Consequently, Ti species are situated in various environments in terms of the oxidation state, dispersion and interaction with donors, which has prevented the understanding of the catalysts.…”

“…In brief, the model catalysts were prepared by treating TiCl 3 ·3pyridine with diethylaluminum chloride (DEAC) in the presence of milled MgCl 2 . Thus, supported TiCl 3 molecules are much less mobile than TiCl 4 , enabling us to control and retain the Ti dispersion state through the Ti content. A lower Ti content results in less interacting or more isolated TiCl 3 molecules, while a higher Ti content leads to more interacting or more agglomerated species.…”

A Comparative Study of AlCl3and FeCl2-Modified TiCl4/MgCl2/THF Catalytic System in the Presence of Hydrogen for Ethylene Polymerization

“…However, a higher Ti content has a higher stereospecificity than a lower Ti content forming an isolated Ti site [29,33,34]. As a consequence, one of the possible reasons was the aggregation of Ti species which caused the reduction of active site concentration, resulting in remarkable depression of the monomer consumption [33] and finally decrease in activity. This result is in good agreement with the report of Taniike et al [33].…”

“…As a consequence, one of the possible reasons was the aggregation of Ti species which caused the reduction of active site concentration, resulting in remarkable depression of the monomer consumption [33] and finally decrease in activity. This result is in good agreement with the report of Taniike et al [33]. They investigated the catalytic performance through the isolated and clustered Zeigler-Natta catalysts in ethylene and propylene homopolymerization.…”